For peace of mind, allow at least 2 hours before short-haul flights when departing for Gatwick, and more for long-haul

https://lorenzogzgk427.yousher.com/gatwick-airport-journey-planner-tools-and-tips-to-pick-the-right-route-3

For peace of mind, allow at least 2 hours before short-haul flights when departing for Gatwick, and more for long-haul. Add buffers for rush hour or weekend engineering.